Thermogravimetric and kinetic analyses of oil palm empty fruit bunch (OPEFB) pellets using the distributed activation energy model

The thermal degradation behaviour and decomposition kinetics of oil palm empty fruit bunch (OPEFB) pellets were investigated using a thermogravimetric analyser and the distributed activation energy model (DAEM). The OPEFB pellets were heated from 30°C to 1000°C at three different heating rates (5, 10, 20°C min-1) under a nitrogen atmosphere. The thermogravimetric-derivative thermogravimetric (TG-DTG) curves revealed that the non-isothermal decomposition of OPEFB pellets occurred in the following three stages: drying (35°C-175°C), active pyrolysis (200°C-370°C) and passive pyrolysis (370°C-1000°C), which resulted in the loss of moisture, volatile matter and char, respectively. The distributed activation energy model was subsequently used to determine the apparent activation energies (E) and pre-exponential factors (A), which ranged from 37.89 kJ mol-1 to 234.05 kJ mol-1 and from 2.05 × 102 min-1 to 3.54 × 1018 min-1, respectively, for conversions of α = 0.05-0.70 during the thermal degradation. The wide E and A distributions obtained from the kinetic analysis are attributed to the complex chemical reactions of pyrolysis. The kinetic analysis revealed the kinetic compensation effect (KCE), with the highest E and A values occurring in the range of α = 0.2-0.4. This result indicates that the active pyrolysis stage is the rate-determining step during the thermal decomposition of OPEFB pellets

Hydrogen production from phenol steam reforming over Ni-Co/ZrO2 catalyst: effect of catalyst dilution

This study looked into the hydrogen production from phenol steam reforming over Zirconia (ZrO2)-supported nickel-cobalt catalysts diluted with silicon carbide (SiC). The objective of this study is to obtain the effect of catalyst dilution on hydrogen production and the phenol conversion in various SiC dilutions. The catalysts were prepared by impregnation method and their performance tests were carried out in a micro fixed bed reactor at atmospheric pressure and 800 °C temperature, feed flow rate 0.36 mL/min, weight of catalyst 0.2 g, and dilution range of 0.05 to 0.35 g (1:0 to 1:1.75). The results showed that the catalyst dilution does not affect much on the catalyst activity toward phenol conversion. However, it does improve the conversion of phenol with the presence of SiC. The maximum conversion was at 0.3 g (1:1.5) SiC dilution, which was of 98.9 % and 0.6 mole fraction of hydrogen

Gasification of oil palm empty fruit bunches (OPEFB) briquettes for bio-syngas production

Gasification of Oil Palm Empty Fruit Bunches (OPEFB) briquettes was investigated in an air blown 4.5 kW allothermal fluidized bed gasifier to examine the effects of bed temperature (600-800 °C) and equivalence ratio (λ = 0.25) on bio-syngas yield and composition. In addition, physicochemical and thermochemical characterization of the fuel properties of the OPEFB briquettes were also examined. The results demonstrate that pelletization improved the solid biomass fuel (SBF) properties of OPEFB including moisture content and higher heating value (HHV). The gasification of OPEFB briquettes produced bio-syngas comprising H2, CO, CO2, CH4 as well as solid biochar with a HHV higher than the original OPEFB briquettes. The highest yield of H2 was obtained at 600 °C while HHV of the bio-syngas was within the range 4-8 MJ/Nm3 for air gasification in fluidized bed gasifiers. In addition, agglomeration of bed materials did not occur during OPEFB briquettes gasification despite its high bed agglomeration potential (BAP). In conclusion, the gasification of OPEFB briquettes into bio-syngas and biochar is a practical route for bioenergy production in Malaysia

Anisotropic Local Stress and Particle Hopping in a Deeply Supercooled Liquid

The origin of the microscopic motions that lead to stress relaxation in deeply supercooled liquid remains unclear. We show that in such a liquid the stress relaxation is locally anisotropic which can serve as the driving force for the hopping of the system on its free energy surface. However, not all hopping are equally effective in relaxing the local stress, suggesting that diffusion can decouple from viscosity even at local level. On the other hand, orientational relaxation is found to be always coupled to stress relaxation.Comment: 4 pages, 3 figure

Energy landscape - a key concept for the dynamics of glasses and liquids

There is a growing belief that the mode coupling theory is the proper microscopic theory for the dynamics of the undercooled liquid above a critical temperature T_c. In addition, there is some evidence that the system leaves the saddlepoints of the energy landscape to settle in the valleys at this critical temperature. Finally, there is a microscopic theory for the entropy at the calorimetric glass transition T_g by Mezard and Parisi, which allows to calculate the Kauzmann temperature from the atomic pair potentials. The dynamics of the frozen glass phase is at present limited to phenomenological models. In the spirit of the energy landscape concept, one considers an ensemble of independent asymmetric double-well potentials with a wide distribution of barrier heights and asymmetries (ADWP or Gilroy-Phillips model). The model gives an excellent description of the relaxation of glasses up to about T_g/4. Above this temperature, the interaction between different relaxation centers begins to play a role. One can show that the interaction reduces the number of relaxation centers needed to bring the shear modulus down to zero by a factor of three.Comment: Contribution to the III Workshop on Nonequilibrium Phenomena in Supercooled Fluids, Glasses and Amorphous Materials, 22-27 September 2002, Pisa; 14 pages, 3 figures; Version 3 takes criticque at Pisa into account; final version 4 will be published in J.Phys.: Condens.Matte

The Glass Transition Temperature of Water: A Simulation Study

We report a computer simulation study of the glass transition for water. To mimic the difference between standard and hyperquenched glass, we generate glassy configurations with different cooling rates and calculate the $T$ dependence of the specific heat on heating. The absence of crystallization phenomena allows us, for properly annealed samples, to detect in the specific heat the simultaneous presence of a weak pre-peak (``shadow transition''), and an intense glass transition peak at higher temperature. We discuss the implications for the currently debated value of the glass transition temperature of water. We also compare our simulation results with the Tool-Narayanaswamy-Moynihan phenomenological model.Comment: submitted to Phys. Re

Resource Competition on Integral Polymatroids

We study competitive resource allocation problems in which players distribute their demands integrally on a set of resources subject to player-specific submodular capacity constraints. Each player has to pay for each unit of demand a cost that is a nondecreasing and convex function of the total allocation of that resource. This general model of resource allocation generalizes both singleton congestion games with integer-splittable demands and matroid congestion games with player-specific costs. As our main result, we show that in such general resource allocation problems a pure Nash equilibrium is guaranteed to exist by giving a pseudo-polynomial algorithm computing a pure Nash equilibrium.Comment: 17 page

Time-temperature superposition in viscous liquids

Dielectric relaxation measurements on supercooled triphenyl phosphite show that at low temperatures time-temperature superposition (TTS) is accurately obeyed for the primary (alpha) relaxation process. Measurements on 6 other molecular liquids close to the calorimetric glass transition indicate that TTS is linked to an $\omega^{-1/2}$ high-frequency decay of the alpha loss, while the loss peak width is nonuniversal.Comment: 4 page

Scaling behavior in the β\beta-relaxation regime of a supercooled Lennard-Jones mixture

We report the results of a molecular dynamics simulation of a supercooled binary Lennard-Jones mixture. By plotting the self intermediate scattering functions vs. rescaled time, we find a master curve in the $\beta$-relaxation regime. This master curve can be fitted well by a power-law for almost three decades in rescaled time and the scaling time, or relaxation time, has a power-law dependence on temperature. Thus the predictions of mode-coupling-theory on the existence of a von Schweidler law are found to hold for this system; moreover, the exponents in these two power-laws are very close to satisfying the exponent relationship predicted by the mode-coupling-theory. At low temperatures, the diffusion constants also show a power-law behavior with the same critical temperature. However, the exponent for diffusion differs from that of the relaxation time, a result that is in disagreement with the theory.Comment: 8 pages, RevTex, four postscript figures available on request, MZ-Physics-10

District flood vulnerability index: urban decision-making tool

Flood vulnerability assessment as an essential part of the urban flood management is done by various methods by several researchers. In fact, the improvement in assessment methods is related to the necessity for enhanced decision-making procedures; for instance, economic or infrastructural investments in cities can be assigned in the best form. To achieve this aim, introducing indices for evaluating vulnerability and identifying more vulnerable zones and then doing relevant comparisons can be useful. District flood vulnerability index (DFVI) developed by the author uses 25 indicators in its calculation. Nevertheless, it is obvious that some of these indicators have no effect on the consequences. This paper presents the results of the analysis for the selection of the most significant indicators of the DFVI construction. This index is appropriate for urban district scaling (or: the urban district scale) and the various components of flood vulnerability (social, economic, environmental and physical). DFVI was made by analyzing the indicators’ relevance and by studying the main indicators needed to depict reality of the urban district floods in an effective way. For this purpose, expert elicitation was done by Delphi and AHP method in two separate phases. Then, all these results were combined in order to construct DFVI equations. Finally, the index was implemented in Kuala Lumpur city’s districts. This paper outlines which district of cities (in this case Kuala Lumpur) are most vulnerable to flood hazard with regard to the system’s components, that is, social, physical, environmental and economic